The optimization relies on CMP setting the destination to 0, which is equivalent to 0.0f. However, early platforms only set the least significant byte, leaving the other bits undefined. So, we must disable the optimization on those platforms.
Oddly, Sandybridge wasn't reported as broken, even though it's documented to only set the LSB. It's unclear whether it follows ILK on IVB behavior. +32 piglits on Ironlake. Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?=79963 Signed-off-by: Kenneth Graunke <kenn...@whitecape.org> --- src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp b/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp index f22d38d..33cb9a9 100644 --- a/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp +++ b/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp @@ -1135,6 +1135,13 @@ vec4_visitor::try_emit_mad(ir_expression *ir) bool vec4_visitor::try_emit_b2f_of_compare(ir_expression *ir) { + /* This optimization relies on CMP setting the destination to 0 when + * false. Early hardware only sets the least significant bit, and + * leaves the other bits undefined. So we can't use it. + */ + if (brw->gen < 7) + return false; + ir_expression *const cmp = ir->operands[0]->as_expression(); if (cmp == NULL) -- 1.9.2 _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
